Glomerular disease is the third leading cause of end stage renal disease in the US, with its related health care costs estimated at $4.1 billion annually. Nephrotic syndrome (NS), characterized by podocyte injury, is one of the most common forms of glomerular disease. Importantly, progressive podocyte injury and loss are also known to be critical determinants of glomerular disease progression. Since the signaling pathways in podocytes most critical for regulation of injury are not yet known, there is an urgent need to better understand which pathways are most able to regulate podocyte injury and recovery to enable the development of more targeted and effective therapies for NS. Our long-term goal is to define specific molecular signaling pathways able to regulate podocyte injury in NS to develop more targeted and less toxic therapies for NS. The overall objective of this proposal is to determine the ability of the glucocorticoid receptor (GR), peroxisome proliferator-activated receptor ? (PPAR?), and MAPK signaling pathways to regulate podocyte injury, and to exploit this knowledge to develop more effective novel therapies for NS. Based on this, we hypothesize that specific manipulation of the GR and PPAR? nuclear receptor pathways and MAPK pathways, and cross-talk among them, will reduce podocyte injury during NS. The rationale for the proposed studies is that specific manipulation of GR-, PPAR?-, and MAPK-mediated pathways or cross-talk among them can ameliorate glomerular injury in NS, and will enable the development of more effective novel approaches to treat NS in the future. To test our hypothesis, we propose the following Specific Aims: 1) To determine if manipulation of critical components of GR and PPAR? nuclear receptor signaling can enhance podocyte protection from injury, 2) To determine the extent and biologic significance of cross-talk among the GC-, TZD-, and MAPK-mediated signaling pathways during podocyte injury, and 3) To determine if manipulation of GC-, TZD-, and MAPK-mediated signaling can ameliorate glomerular injury in animal models of NS. These studies will identify specific potential targets for future drug therapy in NS, and potentially many other glomerular diseases where podocyte injury plays a central role. Validation of these podocyte signaling components as potential drug targets will guide the development of more targeted, more effective, and less toxic therapies for one of the most common kidney diseases in the US.